1. Field of Invention
The present invention relates to a fan and an impeller thereof, which has a flexible portion for dynamically adjusting the angle of attack (AOA) of the blade so as to decrease areas of the stall region.
2. Related Art
An axial-flow fan can induce airflows by rotating its impeller to form a pressure drop. As shown in FIGS. 1 and 2, the blades 12 are fixed wings disposed around the hub 11. Therefore, the angle of attack “A” between the blades 12 and the airflow W is fixed. When the impeller 10 rotates, the blades 12 can not have any angle change relative to the hub 11.
In the conventional fan, since the angle of attack of the blade is fixed, a certain period of stall appears during the back-pressure experiment in the wind tunnel. In this stall period, the airflow worked by the blade is very unstable, which results in loud noise and poor heat dissipation property of the fan.